Understanding the Role of Mesoscale Atmosphere-Ocean Interactions in Seasonal-to-Decadal Climate Prediction

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Skillful predictions of year-to-year climate variations would have tremendous value, for instance advanced warning of droughts would help farmers, water managers, and relief agencies cope with the hardships of water scarcity. The extent to which climate variations are predictable in general is not known, but the example of El Nino shows that predictable variations can arise from interactions between the atmosphere and the ocean. Recent research suggests that predictable climate variations could also result from atmosphere-ocean coupling associated with the Gulf Stream and the Kuroshio Current. A critical aspect of the hypothesized coupling is the involvement of small spatial scales, in particular the atmospheric response to the strong and narrow temperature contrasts between the warm waters of the Gulf Stream and Kuroshio currents and the surrounding cold water. Meanwhile the ocean's response to the atmosphere could involve the mesoscale dynamics of sharp ocean fronts, through which surface winds can induce deep vertical motions. Deep motions are important as they can connect the atmosphere with levels in the ocean where variability takes place slowly, thus creating the potential for skillful long-lead prediction.Research conducted here explores the potential for predictability associated with air-sea coupling using climate model simulations performed at high enough resolutions to capture the mechanisms. The research also looks at the potential for high resolution to capture the weather extremes associated with climate variability, for example changes in the distribution of hurricanes and atmospheric rivers associated with El Nino events. Specifically, the Principal Investigators (PIs) perform simulations using the Community Earth System Model (CESM, version 1.3) with 0.25 degree grid spacing for the atmosphere and 0.1 degree spacing for the ocean. The simulations include a 10-member ensemble of uninitialized transient climate simulations from 1920 to 2100, as well as an ensemble of retrospective 5-year climate predictions starting from years between 1982 and 2016. A number of strategies are pursued to explore the impact of small-scale mechanisms, such as experiments in which the sea surface temperatures produced by the ocean model are smoothed before they are fed into the atmospheric model, thereby disabling small-scale interaction mechanisms.Skillful predictions of climate variability could have tremendous societal value, as noted above, thus work to establish the extent to which the climate system is in fact predictable, and the physical mechanisms that determine its predictability, has substantial broader impacts. The broader impacts of the project are also served by open access to the simulations generated in the project, which allows researchers around the world to engage in research on climate system predictability. The PIs also engage in outreach to the research community and the general public through venues including a radio program titled "On the Ocean" and International CLIVAR summer schools. Educational broader impacts come from the PIs' participation in their department's Research Experiences for Undergraduates program, and through the support and training of a postdoctoral associate and a graduate student.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.